Linear vibratory type motors that generally operate upon piezoelectric principals are receiving wider use in areas where small size and low current drain is desired. One application of this invention is in the field of movement of web material where the invention controls web tension and/or velocity values within acceptable ranges. Generally this is accomplished by the use of a feedback device or circuit in conjunction with a controller. An example of such a system is set forth in U.S. Pat. No. 5,616,979, entitled "Vibration Driven Motor Apparatus" by Nishikawa. The invention of that patent is a rotational device called a traveling wave motor that uses external optical encoder for position of the motor's output shaft. The output from the encoder is fed to an up/down counter and is compared with a reference value. Deviation of the output signal from the reference value is used as an error signal that is fed back to a VCO to provide to the motor a corrected drive signal that causes the motor to change its rotational velocity.
In certain applications the aforementioned technique of providing velocity control to a motor is not adequate in that not all vibratory motors are traveling wave motors. In addition, in certain applications the expense associated with using, for example, discrete velocity sensors is not justified by cost, size, and weight constraints. The present invention is directed to a low cost, relatively simple solution that provides velocity control for linear vibratory type motors.